Setting up modem to share net through switch

A simple one for you guys:

How does one go about sharing an internet connection between 2 PCs on a modem and separate switch? I don't know the details of either because I'm asking for a friend, but it's a D-Link ASDL modem and a Belkin switch.

I assume the modem's ethernet cable goes into one port and the two computers in another two... but where does it go from here? I'm guessing they have to access the modem's menu and enable NAT of some kind.

Could anyone give a quick step-by-step runthrough that I can talk them through over the phone?

Cheers.

>>9
cheapest router i can find 'round these parts is still twice as expensive as an average 10/100 PCI network card.  and if he already has a switch, it's mostly redundant hardware.

unless we're talking a total computer n00b who's too scared to open his own case, in which case i would recommend the router as well.